Over the years skid steer loaders have been known as agile, compact vehicles with a high degree of maneuverability and a wide range of applications in the agricultural, industrial and construction fields. These vehicles usually include an engine, a boom assembly and an operators compartment mounted on a frame supported by four wheels. Coupled to the engine are a main drive system and a lift system for the boom assembly. The vehicle is maneuvered by driving the wheels on one side at a different speed and/or in a different direction from those on the other side resulting in a turning motion, the severity of which is determined by the relative speeds.
Typically the engine, which is rear mounted for counterbalancing effect, drives a pair of hydrostatic pumps coupled to left and right mounted hydrostatic motors. Wheels on the left and right sides of the vehicle are driven by the left and right mounted motors through gears, chains and sprockets. In one known control arrangement, motion is controlled by an operator seated within the operators compartment by moving a pair of hand operated control levers which are linked to the pumps. The extent to which each lever is moved in a forward direction from a neutral position controls the amount of fluid supplied in a forward direction to its respective motor, and therefore the speed at which the wheels on that side of the vehicle will rotate. Similarly, the extent to which a lever is moved in the reverse direction from the neutral position will control the speed at which the associated wheels rotate in the reverse direction.
As mentioned above, skid steer loaders include a boom assembly. This assembly generally comprises a pair of lift arms and means for mounting the arms on the main frame. Attachments are usually operatively associated with the front of the lift arms. A separate hydraulic system is used to actuate the boom assembly via hydraulic lift cylinders which drive the lift arms. This system is also used to actuate one or two tilt cylinders which pivot the attachment with respect to the lift arms. In the control arrangement mentioned above, a pair of foot pedals conveniently located in the lower front area of the operator compartment control the flow of hydraulic fluid from a hydraulic pump to the lift and tilt cylinders.
In addition to material handling buckets, various other attachments such as snow blowers, trenchers, tree spades and augers which include their own hydraulic motors are commonly mounted to the boom assembly. An auxiliary hydraulic system is used to control the flow of hydraulic fluid between the hydraulic pump and the hydraulic motor of the front mounted attachment. It is common in prior art systems, using the arrangement mentioned above, for the flow of hydraulic fluid to the motor to be controlled by an auxiliary spool valve through actuation of a pivotally mounted handle on one of the control levers. The handle is normally biased to a neutral position. Pushing the handle (relative to the lever on which it is mounted) in one direction strokes the auxiliary valve in a first direction, thereby causing hydraulic fluid to flow to the front mounted attachment in a first direction. Pushing the handle in the opposite direction strokes the auxiliary valve so as to supply fluid in a reverse direction.
In an alternative prior art control arrangement, flow of hydraulic fluid to the lift and tilt cylinders is controlled by a pair of handles on the control levers. Movement of one handle relative to its respective lever controls the boom lift cylinders and movement of the other handle relative to its respective lever controls the bucket tilt cylinders. In this arrangement, if an auxiliary hydraulic system is used for controlling a hydraulic motor or cylinder for mounted attachments, then a foot pedal is utilized for operator actuation.
Further, with respect to prior art skid steer loaders, it has been found to be advantageous to employ a system that permits the vehicle to operate in high and low speed ranges. For example, when filling the bucket, maximum wheel torque is necessary for effective operation in most conditions. Therefore, a low range of speeds is most useful in this phase of the operation. But, when the dump site is situated a significant distance from the work site, as it often is, a higher range of speeds for transport is desirable, which thereby provides an obvious enhancement to the overall effectiveness of the vehicle. At the dump site the operator may wish to drop back to a lower range for maximum control when simultaneously raising the boom and dumping, such as when approaching and dumping into a truck. Finally, upon completion of such dumping task, the operator can shift back to the high range for travel back to the work site.
An assembly used in a system of the type described above, is illustrated on page 31 of Sperry New Holland Service Parts Catalog for Model L-781, L-784 and L-785 Skid Steer Loaders (1985), printed in U.S.A. and identified by catalog no. 5078132. In this arrangement an operating lever, located in the operator's cab, is coupled to a shaft assembly that moves the hydrostatic motor pintle shafts. When the lever is moved from a first position to a second position, the shaft assembly moves the pintle shafts from a high speed operating mode to a low speed operating mode.
Notwithstanding the successful operation of this prior art system, embodied in various models of skid steer loader vehicles manufactured and sold by the predecessor company of the assignee of the present application, applicants have embraced various needs and problems of that system. The below described invention is a new and useful solution that meets the needs of such prior art system, as well as other systems with similar demands, in a manner not heretofore known.